Summary:
TtdT is a putative tartrate/succinate antiporter belonging to the DASS family of di- and tri-carboxylic acid transporters. The ttdT is located in a probable operon with the ttdAB genes encoding L-tartrate dehydratase. In an analogous manner to CitT [Pos98], under anaerobic conditions TtdT allows the uptake of L-tartrate in exchange for succinate, the end product of tartrate fermentation. In strains lacking anaerobic C4-dicarboxylate antiporters and CitT, TtdT is required for tartrate fermentation as tartrate uptake in ttdT mutants is normal, but tartrate/succinate antiport does not occur [Kim07d, Oshima06a]. Tartrate is taken up in ttdT mutants by some other mechanism, possibly YeaV or YfaV [Kim07d].